CAREER: The onset of the rainy season in Amazonia

亚马逊盆地一直被称为“绿色海洋”，这个词的灵感来自其茂密的森林树冠上翠绿的广袤土地。在雨季，这种类比具有物理意义，因为降雨主要来自中等深度的积云，类似于热带海洋上常见的积云。此外，森林表面为维持云层提供了充足的水分来源，在海洋对流中扮演着与海洋表面相同的角色。但PI之前的研究表明，在旱季结束时，这种类比被打破，云看起来更像是干燥草原上形成的积云塔。地面也扮演着不同的角色，因为深层云是由高对流可用势能(CAPE)触发的，而地面主要是建立CAPE的热源，而不是水汽来源。认识到潮湿和干燥陆地表面的不同作用，首席调查员(PI)考虑了植物生理在爆发前季节(也称为过渡季节)云形成中所起的作用。在旱季结束时，水分胁迫很常见，水分胁迫下的植被保持水分，导致地表升温，促进更高的开普敦。另一方面，云需要水蒸气的来源，在土壤仍然潮湿的邻近地区，水蒸气可以由植物蒸腾提供。因此，PI假设，地表加热在水分胁迫地区引起的上升运动从低水分胁迫地区(植物将水分散发到空气中)吸收水分，因此植物水分胁迫高低之间的梯度在雨季开始时促进对流起到关键作用。研究使用来自卫星遥感和气象再分析产品的观测数据，结合数值模拟，涵盖了将植物生理与云和降水联系起来的一系列现象和空间尺度。一个关键的数据来源是卫星衍生的太阳诱导荧光(SIF)，这是一种由暴露在阳光下的植物中的叶绿素发出的微妙的特定波长的辉光。以前的研究表明，当植物处于水分胁迫下时，SIF会下降，因此来自卫星的SIF可以用来绘制亚马逊地区水分胁迫的空间梯度。这一职业奖的教育部分侧重于向服务不足和代表性不足人群的K-12和大学生进行宣传。在大学层面，PI与领导力联盟暑期研究早期识别方案合作，为少数族裔服务机构的本科生提供暑期实习机会。K-12教育是与普罗维登斯公立学校(PPS)合作解决的，这些学校为高比例的西班牙裔和非裔美国学生提供服务。PI的团队与PPS官员合作，为中小学教师组织暑期研讨会，帮助他们创建和实施关于天气、气候和生态系统相互作用的课程模块。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Amazon basin has been called the "Green Ocean", a term inspired by the emerald expanse of its dense forest canopy. In the rainy season the analogy has physical significance as the rain falls primarily from mid-depth cumulus clouds which resemble those commonly found over tropical oceans. Also, the forested surface provides an abundant source of moisture to sustain the clouds, playing the same role as the ocean surface in maritime convection. But prior work by the PI shows that at the end of the dry season the analogy breaks down and clouds look more like the cumulus towers that form over dry grasslands. The surface also plays a different role, as the deep clouds are triggered by high values of convective available potential energy (CAPE), and the surface serves primarily as a heat source to build CAPE rather than a moisture source.Recognizing the differing roles of moist and dry land surface, the principal investigator (PI) considers the role played by plant physiology in cloud formation during the pre-onset season (also referred to as the transition season). Water stress is common at the end of the dry season and vegetation under water stress retains moisture, causing the surface to heat up and promoting higher CAPE. On the other hand clouds need a source of water vapor, which can be supplied by plant transpiration in adjacent regions where the soil is still moist. Thus the PI hypothesizes that rising motion induced by surface heating over water stressed regions draws in moisture from regions of low water stress (where plants transpire moisture into the air), so that the gradient between high and low plant water stress plays a key role in promoting convection at the onset of the rainy season.The research uses observational data from sources including satellite remote sensing and meteorological reanalysis products, together with numerical simulations, to cover the range of phenomena and spatial scales linking plant physiology with clouds and precipitation. One key data source is satellite-derived Solar Induced Fluorescence (SIF), a subtle and wavelength-specific glow emitted by chlorophyll in plants exposed to sunlight. Previous studies have shown that SIF declines when plants are under water stress, thus SIF from satellites can be used to map the spatial gradient of water stress over the Amazon.The educational component of this CAREER award focuses on outreach to K-12 and college students from underserved and underrepresented populations. At the college level the PI works with the Leadership Alliance Summer Research Early Identification Program to provide summer internships for undergraduates from minority serving institutions. K-12 education is addressed in collaboration with the Providence Public Schools (PPS), which serve a high percentage of Hispanic and African American students. The PI's team works with PPS officials to organize summer workshops for elementary and middle school teachers to assist them in creating and implementing lesson modules on weather, climate and ecosystem interactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.